Chiral liquid crystal compounds

ABSTRACT

This invention relates to novel chiral cyano-containing compounds suitable for use in ferroelectric smectic liquid crystal mixtures.

This is a continuation of application Ser. No. 07/734,105, filed Jul.24, 1991, now abandoned, which is a continuation of Ser. No. 07/305,730filed Feb. 1, 1989, now abandoned.

This invention relates to novel chiral compounds suitable for use inferroelectric smectic liquid crystal mixtures, and to such mixtures anddevices which incorporate them.

Ferroelectric smectic liquid crystal materials use the ferroelectricproperties of the chiral tilted smectic C, F, G, H, I, J and K phases(designated S*_(C) etc., the asterisk denoting chirality). The S_(C)phase is generally the most useful, as it is the most fluid, and it isparticularly desirable that the material shows an S_(A) or nematic(denoted N) phase at temperatures above the chiral smectic phase, toassist surface alignment in a liquid crystal device. Ferroelectricsmectic liquid crystal materials desirably have low viscosity, S_(C)phases that persist over a broad temperature range which includesambient temperature, chemical and photochemical stability, and inparticular have a good spontaneous polarisation coefficient, Ps,measured in nC cm⁻². Such materials offer the possibility of very fastswitched liquid crystal display devices.

Although some single compounds show all of the desirable propertiesoutlined above, ferroelectric smectic liquid crystal materials in usetoday generally consist of a mixture of compounds which together show achiral tilted smectic phase. Some of the compounds in such a mixture areof a type which either together or separately show a smectic phase (notnecessarily being a chiral smectic phase), called a "smectic host", someare additives to improve the properties of the mixture, e.g. to suppressundesirable smectic phases and one or more is an optically activecompound which induces the mixture to be chiral smectic, ideally with agood Ps. Such optically active compounds are called in the art "chiraldopants".

PCT patent application WO 86/00087 describes a series of opticallyactive liquid crystal compounds that contain the chiral groups: ##STR1##where X represents Cl, CN or CH₃ and R₁ and R₂ represent the residue ofthe molecule. All of the compounds described necessarily contain thephenyl-pyrimidine group, ##STR2## as the mesogenic unit. The pyridinering is said to be particularly beneficial in the short moleculesdescribed as its molecular configuration increases intermoleculardistances in the bulk, thus reducing the viscosity. Among the manycompounds described are: ##STR3## These two compounds do not showsmectic phases by themselves.

PCT Application WO 87/05015 describes a series of compounds having ageneral formula ##STR4## where X may be CN, Halogen or CH₃, R¹ and R²may be alkyl or alkoxy, Q¹, Q², Z¹ and Z² are linking groups and A¹, A²and A³ are cyclic groups (e.g. phenyl etc.). No examples of compoundswhere X is CN are described, and a preference for X being halogen isexpressed.

It is an object of the present invention to provide further compoundshaving advantageous properties for use in ferroelectric smectic liquidcrystal mixtures. Other objects and advantages of the present inventionwill become apparent from the following account.

According to a first aspect of the invention there is provided aferroelectric smectic liquid crystal mixture containing at least twocompounds at least one of which is an optically active dopant compoundhaving a general formula I below: ##STR5## in which X is a group havinga general structure: ##STR6## where R is selected from hydrogen or C₁₋₁₂alkyl or alkoxy, each of the rings ##STR7## is the same or different andis each independently selected from phenyl, halogen-substituted phenylor trans cyclohexyl, A is selected from a single bond, COO or OOC, a is0 or 1, Y is selected from COO or O, and B is alkyl containing 1-12carbon atoms, cyclohexyl or a group ##STR8## where d is 0 or 1 and R' isselected from hydrogen or C₁₋₁₂ alkyl or alkoxy.

Many compounds of Formula I are useful as chiral dopants inferroelectric smectic liquid crystal mixtures with a host component.

The relative usefulness of various compounds of Formula I is one of thefactors determining the structural and other preferences discussedherein.

In Formula I, R is preferably alkyl or alkoxy, containing 1 to 20 carbonatoms, especially n-alkyl or alkoxy containing 7 to 10 carbon atoms.Alkoxy is more preferred.

When --Y--CH(CH)-- is present as --COO--CH(CN)-- it is particularlypreferred that B is cyclohexyl or alkyl.

When B is alky it may be n-alkyl, branched alkyl or optically activealkyl. The branching in the branched alkyl chain may be at any point sothat when B is branched or optically alkyl it may have a structure B':##STR9## where t may be 0 or an integer 1-6 and n and m may be the sameor different and have values 1-6. Preferably t is 0 or 1 and at leastone of n or m is 1.

Preferred alkyl groups from which B may be selected are listed below intable 1.

                  TABLE 1                                                         ______________________________________                                        CH.sub.3  CH(CH.sub.3)2  CH2CH(CH.sub.3)2                                     C.sub.2 H.sub.5                                                                         CH(CH.sub.3)C.sub.2 H.sub.5                                                                  CH.sub.2 CH(CH.sub.3)C.sub.2 H.sub.5                 C.sub.3 H.sub.7                                                                         CH(CH.sub.3)C.sub.3 H.sub.7                                                                  CH.sub.2 CH(CH.sub.3)C.sub.3 H.sub.7                 C.sub.4 H.sub.9                                                                         CH(CH.sub.3)C.sub.4 H.sub.9                                                                  CH.sub.2 CH(CH.sub.3)C.sub.4 H.sub.9                 C.sub.5 H.sub.11                                                                        CH(CH.sub.3)C.sub.5 H.sub.11                                                                 CH.sub.2 CH(CH.sub.3)C.sub.5 H.sub.11                C.sub.6 H.sub.13                                                                        CH(CH.sub.3)C.sub.6 H.sub.13                                                                 CH.sub.2 CH(CH.sub.3)C.sub.6 H.sub.13                C.sub.7 H.sub.15                                                                        CH(CH.sub.3)C.sub.7 H.sub.15                                                                 CH.sub.2 CH(CH.sub.3)C.sub.2 H.sub.15                C.sub.8 H.sub.17                                                                        CH(CH.sub.3)C.sub.8 H.sub.17                                                                 CH.sub.2 CH(CH.sub.3)C.sub.8 H.sub.17                C.sub.9 H.sub.19                                                                        CH(CH.sub.3)C.sub.9 H.sub.19                                                                 CH.sub.2 CH(CH.sub.3)C.sub.9 H.sub.19                C.sub.10 H.sub.21                                                                       CH(CH.sub.3)C.sub.10 H.sub.21                                       ______________________________________                                    

Particularly preferred alkyl groups in table 1 are underlined.

Some examples of preferred groups X in formula I, especially where--Y--W--CH(Z) is --COOCH(CN)-- and with the preferred B groups arelisted in table 2 below:

                  TABLE 2                                                         ______________________________________                                         ##STR10##                     2.1                                             ##STR11##                     2.2                                             ##STR12##                     2.3                                             ##STR13##                     2.4                                             ##STR14##                     2.5                                             ##STR15##                     2.6                                             ##STR16##                     2.7                                             ##STR17##                     2.8                                             ##STR18##                     2.9                                            ______________________________________                                    

where R is n-alkyl or n-alkoxy, especially containing 3-12 carbon atoms.Of these structures 2.1 to 2.7 are preferred.

Some particularly preferred overall structures for the compound offormula I are therefore listed below in table 3

                  TABLE 3                                                         ______________________________________                                         ##STR19##                     3.1                                             ##STR20##                     3.2                                             ##STR21##                     3.3                                             ##STR22##                     3.4                                             ##STR23##                     3.5                                             ##STR24##                     3.6                                             ##STR25##                     3.7                                             ##STR26##                     3.8                                             ##STR27##                     3.9                                            ______________________________________                                    

where R₁ is C₃ -C₁₂ n-alkyl or n-alkoxy and R₂ is C₁ -C₁₂ n-alkyl or abranched or optically active alkyl group of structure B' especiallythose structures listed in table 1, and (F) indicates that a fluorinesubstituent may be present.

The chiral centre(s) in a compound of formula I may be of (R) or (S)configuration, and if the compound contains more than one chiral centrethen preferably these are such as to induce the formation of S* phaseshaving the same sign of Ps in a ferroelectric smectic mixture in whichthey are included.

Compounds of formula I in which the unit --Y--CH(CN)-- is COO CH(CN) maybe prepared for example by a number of widely applicable routes 1-5shown schematically in FIGS. 1-5. Compounds of formula I in which--Y--CH(CH)-- is --OCH(CN) may be prepared for example by route 6 shownin FIG. 6.

In routes 1-6 the group B is in some cases introduced into the compoundof formula I using an alpha-hydroxy carboxylic acid of formula:##STR28## or an alpha-amino acid in formula: ##STR29##

Routes 1-6 are of general suitability but are particularly suited tocases where B is alkyl, phenyl or cyclohexyl.

Some of these acids are commercially available in an optically pureenantiomeric form, e.g. the hydroxy carboxylic acids lactic acid (B═CH₃)and mandelic acid (B=phenyl), and the series of commercially availableor naturally occurring amino acids, e.g. alanine, valine, leucine,isoleucine, butyrine, alloisoleucine, norvaline, norleucine andphenylalanine. As many such acids are of biochemical origin, they areoften available in optically pure forms of one or more enantioners orantipodes, thus yielding optically pure products, whilst at the sametime being relatively cheap. The use of these acids where possible istherefore preferred.

Alternatively these acids may be synthesized, to lead to a wider rangeof B-groups. The alpha-hydroxy acids may in fact be prepared from thecorresponding amino acids by reaction of the amino acid with nitrousacid at low temperatures: ##STR30## (e.g. "Tetrahedron" (1979), 35, 1603and J.A.C.S. (1956) 78, 2428).

Other methods of preparation of alpha-hydroxy carboxylic acids are wellknown, for example as described in "Chemistry of Carbon Compounds" ed D.H. Dodd (pvb Elsevier) (1952), IB, p 780-781 (Ref 1) which lists 11methods of preparation, including those where B may be straight chain,branched chain or optically active alkyl.

Similarly the amino acids having an appropriate B group may besynthesized be general well known methods, for example as described inRef 1 p 813-817, where 13 methods for the synthesis of a wide range ofamino acids is described, including those where B is straight chain,branched chain or optically active alkyl.

Preparation of a suitable alpha hydroxy or amino acid should thereforepresent no difficulty to the competent chemist. Where these preparationmethods result in racemic mixtures of the optical enantiomers orantipodes they may be resolved by known methods, e.g. the use of brucineor steroespecific enzymic reactions.

When the amino acid used to pre pare the alpha-hydroxy acid or useddirectly e.g. in route 4 contains functional groups in its side chain B,these may be used to vary the structure of the group B.

For example serine, threonine and tyrosine contain --OH groups in theirside chain, which enables the introduction of ester or ether linkages.Aspartic and glutamic acid contain --COOH groups in their side chainwhich also enable ester or other linkages to be introduced.

Examples of the types of unit which can be introduced into a compound offormula I using amino acids with functional groups in the side chaininclude: ##STR31##

Similarly where routes 1-6 below require the use of a carboxylic acid ofgeneral structure R--X--CO₂ H (where X is as defined in formula I) manyof these are commercially available or else may be synthesised by wellknown general methods for example hydrolysis of the corresponding cyanocompounds R--X--CN.

The individual steps of routes 1-6 are identified below.

Route 1

The steps are identified below:

(1)

(i) 20% aqueous Cs₂ CO₃ or K₂ CO₃, methanol-water (9:1) pH 7.0

(ii) Ph CH₂ Br, DMF.

(2) N,N-dicyclohexylcarbodiimide (DCC), 4-(N-pyrrolidino)pyridine(N--PPy), CH₂ Cl₂.

(3) 5% Pd/C, hydrogen, ethanol.

(4)

(i) oxalyl chloride, benzene, dimethylformanide (DMF).

(ii) aqueous ammonia, diglyme.

(5) SOCl₂, DMF.

Although it is illustrated for use with 4-alkyl- oralkoxybiphenyl-4'-carboxylic acid, Route 1 is generally suitable for allacids of formula R--X--CO₂ H and particularly suitable for those groupsX which contain rings ##STR32## linked by single bond. By the use oflactic acid in step (1) B is caused to be methyl, but other homologousalpha-hydroxy carboxylic acids may be used to cause B to be other alkylgroups. By the use of mandelic acid, i.e. ##STR33## B may be caused tobe phenyl.

Route 2

(1) ##STR34## ethyl acetate, hydrogen chloride.

(2) KOH, ethanol, water

(3) similar to Route 1 steps (1) and (2)

(4) oxalic acid, 90% aqueous ethanol

(5) similar to Route 1 step (2)

(6) a series of steps analogous to route 1 steps (3)-(5)

As with roure 1, this route is generally applicable to compounds offormula I where one of the groups A in X is COO. By using otheralpha-hydroxy acids, different groups B may be introduced into themolecule, as discussed above.

Route 3

(1) hydrogen, 5% Rh/Al₂ O₃, methanol

(2) as route 1 step (1) using methanol solvent.

(3) ##STR35## DCC, N--PPy, CH₂ Cl₂ (R=alkyl or alkoxy)

(4) hydrogen, 5% Pd--C, ethanol.

(5)

(i) (COCl)₂, benzene, DMF

(ii) aqueous ammonia diglyme.

(6) SOCl₂, DMF.

Route 4

(1) Sodium Nitrite, H₂ SO₄

(2) PhCH₂ Br, DMF (Ph=phenyl)

(3) DCC, N--PPY, CH₂ Cl₂

(4) H₂ /Pd--C

(5) Oxalyl Chloride, DMF; NH₃

(6) SOCl₂, DMF

Although route 4 is shown for a case where X is an R-biphenyl group, themethod works equally well using any appropriate carboxylic acid in step(3).

In route 4, the group B in the starting amino acid is the group B of thefinal product. The amino acid may be used in any of its enantiomericforms (a racemic amino acid would lead to a racemic product). Theresidue B in the starting amino acid may itself contain an asymmetriccarbon atom, for example in the case of isoleucine.

Various other compounds wherein the unit --YWCH(Z)-- is --COO CH(CN)--may be made via routes derived from routes 1-4 above. For examplecompounds of structure 3.4 may be made by esterifying the product ofstep 3(2) with the acid produced in step 2(2) and proceeding via a routeanalogous to steps 2(3) to 2(6).

Compounds of structure 3.5 may be prepared via route 5 shown in FIG. 5starting from the commercially available biphenyl and bromobenzoic acid.

Route 5

(1) When the F is present: n--BuLi, ether, -35° C., 20 min, ZnCl₂, THF,N₂. When the F is not present: n--BuLi, ether, -5° to -10° C., 45 min;ZnCl₂, THF, N_(c).

(2) An appropriate alcohol or phenol, e.g. the product of steps 4(2) or3(2), DCC, N--PP_(y), CH₂ Cl₂.

(3) Pd[Ph₃ P]₂ Cl₂, di-isobutylaluminium hydride, THF N₂.

The product of step 5(3) may then be converted to the cyano compounde.g. of structure 3.5 by a method analogous to steps 4(4)-4(6).

Route 6

(1) esterification of the alpha-hydroxy acid using e.g. DCC method. Somesuch esters may be commercially available, e.g. ethyl lactate.

(2) toluene-4-sulphonyl chloride, pyridine.

(3) K₂ CO₃, acetonitrile.

(4) KOH, ethanol, H₂ O.

(5) and (6), as steps 4(5) and (6)

Compounds of formula I may be used as optically active components offerroelectric smectic liquid crystal mixtures, i.e. as chiral dopants.When used as components of such mixtures compounds of formula I,particularly the preferred compounds referred to above, may offer thefollowing advantages.

(i) They may show a very high spontaneous polarisation coefficient (Ps).This may conveniently be expressed in terms of the extropolated Ps, i.e.the Ps of the mixture extropolated to 100% of the compound of formula I.This means that a quite a small amount of the compound of formula I needbe included in the mixture.

(ii) They may induce the appearance of chiral smectic phases in themixture having a very long helical pitch. This may more conveniently beassessed by measuring the chiral nematic N* pitch they induce when mixedwith a nematic liquid crystal materal. A long pitch is desirable as insome ferroelectric smectic liquid crystal devices the pitch should be asclose as possible to the spacing of the electrodes, and in practice thedifficulty of manufacture increases with decreasing electrode spacing.

(iii) Chiral smectic mixtures containing them may show Sc* phases whichpersist over a wide temperature rnage, including room temperature.

(iv) They are compatible with many hosts and additives for example thosediscussed below.

(v) They may offer the possibility of very high switching speeds, whichis of advantage in for example video screen type applications. This ispartly due to (i) above in that many known chiral dopants are viscousand cause mixtures containing them to be viscous. The good Ps induced bycompounds of formula I means that relatively little need be used andhence there is little adverse effect on viscosity.

(vi) It is often possible to obtain compounds of formula I in both D(+)and L(+) enantiomeric forms as both enantioneric forms of the startingamino acid for their preparation may be available. This makes the pitchof mixtures containing them to be particularly easy to "compensate" (seebelow) by including opposite-twisting enantiomers of the compounds offormula I in the mixture.

A ferroelectric smectic liquid crystal mixture according to theinvention contains at least one compound of formula I. Typically themixture will contain 1-20% by weight of the compound of formula I, e.g.around 10% or less. Generally the Ps of the mixture is proportional tothe amount of chiral dopant present.

The mixture should contain one or more compounds which either separatelyor together shown an Sc phase. Such compounds are known as smectichosts.

A large number of classes of compounds which may be used as smectichosts are known, and some examples of suitable classes are listed intable 4. Of these compounds those of formula 4.1, 4.2, 4.3, and 4.8 arepreferred, especially where R^(A) and R^(B) independently contain 5-10carbon atoms. It is particularly preferred to use a mixture of two ormore members, e.g. homologues, of the same class for example to reducethe melting point.

These preferred hosts allow the possibility of Sc mixtures showing an Scphase persisting over a wide temperature range including roomtemperature, and also an S_(A) phase at a temperature above the Sc, toassist in alignment of the liquid crystal material. Typically themixture will contain 40-99% of host compounds, e.g. around 80%.

                  TABLE 4                                                         ______________________________________                                         ##STR36##                     4.1                                             ##STR37##                     4.2                                             ##STR38##                     4.3                                            racemic                                                                        ##STR39##                     4.4                                            racemic                                                                        ##STR40##                     4.5                                             ##STR41##                     4.6                                             ##STR42##                     4.7                                             ##STR43##                     4.8                                            ______________________________________                                         where R.sup.A and R.sup.B are C.sub.1-12 nalkyl or nalkoxy.              

Additives in such a mixture may serve a number of functions. One suchfunction is as "pitch compensators." "Pitch compensation" is theinclusion in the ferroelectric smectic mixture of two or more compoundswhich induce the appearance of helical smectic phases of opposite twistsense. In such a case the compounds will unwind the helical phaseinduced by the other. This may be used to produce along pitch helicalsmectic phase, and by the controlled use of appropriate quantities ofthe two compounds the pitch of the mixture may be closely controlled.

In mixtures according to the invention, pitch compensation may beachieved conveniently by using opposite-twisting compounds of formula Ias discussed above which may be different compounds of formula I orenantiomers e.g. the L(+) and S(+) forms of the compound ##STR44##

Alternatively or additionally other optically active additives may beused, for example the amides described in PCT/GB 87/00223, e.g. any ofthose listed in table 6 thereof, or the terphenyls described in UKPatent Application 8703103, the latter being particularly suitable whenthe host includes one or more compounds of formula 4.3.

Examples of pitch compensators of these two types include the compounds:##STR45## where R and R' are independently C₁₋₁₂ n-alkyl or n-alkoxy. F'is preferably CH₃. Many other pitch compensating additives will beapparent to those skilled in the art. For example when the host containsone or more compounds of formula 4.1 or 4.2, a suitable pitchcompensator may be a compound of formula 4.1 or 4.2 where R^(B) or/andR^(A) are optically active alkyl or alkoxy.

Additives may be used to encourage the appearance of an S_(A) phase at atemperature above that at which the S_(C) * phase persists, to assist inalignment of the S_(C) * phase during assembly of the service. When thehost consists largely of compounds of formula 4.1 or 4.2, preferredadditives to achieve this have a formula: ##STR46## where R and R¹ areindependently n-alkyl or n-alkoxy containing 1-12 carbon atoms,especially 5-9.

Additives may alternatively serve the function of suppressingundesirable smectic phases such as S_(A) or S_(B) so that these appear,if at all, as far as possible from the working temperature range. Apreferred class of additives fulfilling this function are the esters offormula: ##STR47## where R and R¹ are independently n-alkyl or n-alkoxycontaining 1-12 carbon atoms, especially 5-9. Compounds of formula 4.8may also be used as additives to suppress undesirable smectic phases inmixtures where they are not used as hosts.

Additives may also improve other properties of the mixture, for exampleto increase the switching speed. Compounds which do this include thosewhich contain a ##STR48## group, for example those of general formula##STR49## where R and R¹ are independent alkyl groups especiallycontaining 3 to 10 carbon atoms.

Other known additives may be included, for example to improve viscosity,melting point or other properties.

Typically a mixture according to the invention may contain 0-50wt % ofadditives, preferably 0-20%. Only minute amount of pitch compensatorsmay be necessary, e.g. less than 1 wt % of the tight twisting compound5.1 where R is C₁₀ H₂₁ and R¹ is CH₃, and preferably no more than about10 wt % of compounds such as 6, 7, 8.1 or 8.2.

A mixture according to the invention may be used in any of the knowntypes of ferroelectric smectic liquid crystal electro-optic device, anda device incorporating such a mixture is another aspect of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described by way of example only withreference to the accompanying drawings, which show:

FIGS. 1-6 preparative routes for compounds of the invention.

FIG. 7 graphs of Ps against temperature for mixtures of the invnetion.

FIG. 8 a liquid crystal device.

Examples of methods of preparation of compounds of Formula 1, offerroelectric smectic liquid crystal materials including them and of aliquid crystal electro-optic display device using them follow.

EXAMPLE 1

Preparation of; ##STR50## using Route 1

Step 1(1)

S-(+)-Lactic acid (18.0 g) (previously redistilled from commercialproduct) was dissolved in methanol (360 ml), and water (40 ml) wasadded. The solution was trated to pH 7-0 with 20% aqueous caesiumcarbonate (ca 160 ml). The solvent was removed under reduced pressure at50° C. and the residue was re-evaporated twice from DMF (2×100 ml) atthe same temperature. The white solid caesium salt obtained was stirredwith benzyl bromide (34.2 g) in DMF (300 ml) for 15 hours. The CsBr wasthen filtered off, the filtrate was concentrated and then ether wasadded to the residue (150 ml). The organic layer was washed successivelywith water (100 ml), saturated Na NHO₃ (500 ml) and water (100 ml) andfinally dried (MgSO₄). After removal of the solvent the residual liquidwas distilled under reduced pressure to afford the product ascoulourless liquid (yield 28.8 g; 80%), bp 96° C./0.05 mm Hg[ α]_(D) ²⁴-12.9°.

Step 1(2)

To a stirred mixture of 4-R-biphenyl-4'-carboxylic acid (10.8 g),S-(-)-benzyl lactate (5.9 g) prepared as in step 1(1) above, and N--PPy(0.49 g) in sieve-dried (CH₂ Cl₂ (250 ml) was slowly added a solution ofDCC (7.5 g) in sieve dried CH₂ Cl₂ (50 ml). The mixture was stirred for5 h at room temperature. The N,N-dicyclohexyl urea was filtered off andthe filtrate was washed successively with water (100 ml), 5% aqueousacetic acid (100 ml), water (2×100 ml) and finally dried (MgSO₄). Afterremoval of the solvent, the crude diester was purified by columnchromatography using silica gel and (4:1) dichloromethane: petroleumfraction (bp 60°-80° C.) as eluent. The product was recrystallised fromethanol

The properties of compounds prepared in this way were:

R═C_(q) H₁₉ : mp 60.5° C.; [α]_(D) ²⁴ +21.6°.

R═C₁₀ H₂₁ O: mp 85° C.; [α]_(D) ²⁴ +24.2°.

R═C₈ H₁₇ O: mp 62.5° C.; [α]_(D) ²⁴ +24.7°.

Step 1(3)

The product of step 1(2) (10-12 g) was dissolved in ethyl acetate (150ml). 5% Pd on charcoal (200 mg) was added and the mixture was stirredunder an atmosphere of hydrogen overnight. After hydrogenation (500 mlof hydrogen was consumed) was completed, the catalyst was filtered offand the filtrate was evaporated to dryness. The colourless solid residuewas recrystallised from petroleum fraction (bp 60°-80° C.) to give thecarboxylic acid as colourless needles.

R═C₉ H₁₉ : mp 106° C.; [α]_(D) ²⁴ +32.3°.

R═C₁₀ H₂₁ O: mp 115° C.; [α]_(D) ²⁴ +35.0°.

R═C₈ H₁₇ O: mp 126° C.; [α]_(D) ²⁴ +40.8°.

Step 1(4)

The carboxylic acid of step 1(3) (0.01 mol) was initially converted intothe acid chloride by reacting with oxalyl chloride (0.02 mol) andsieve-dried DMF (3 drops) in sodium-dried benzene (50 ml) for 3 hours atroom temperature. The excess of oxalyl chloride and the solvent wereremoved by distillation under reduced pressure. The crude acid chlorideresidue was dissolved in diglyme (20 ml) and then an aqueous solution ofammonia (25 ml, d=0.88) was added dropwise with vigorous stirring. Afterthe addition the reaction mixture was stirred for 11/2 hours atroom-temperature. The reaction mixture was then diluted with cold water(200 ml) and the product was filtered off, washed with excess water andthen finally dried in air. The product was crystallised from petroleumfraction (bp 80°-100° C.) to yield the amide as a white powder.

R═CH₉ H₁₉ : yield=2.6 (66%); mp 145° C.; [α]_(D) ²⁴ +48°.

R═C₁₀ H₂₁ O: yield=1.8 g (47%); C₁ 130 C₂ 143 I[α]_(D) ²⁴ +43.4.

Step 1(5)

A mixture of redistilled thionyl chloride (0.063 mol) and sieve-driedDMF (10 ml) was added dropwise to a vigorous stirred solution of theproduct of step 1(4) (0.0063 mol) in DMF (30 ml). After the addition thereaction mixture was stirred at room temperature for 2 hours, pouredonto ice-water (200 ml) and the product extracted into ether (2×100 ml).The combined ether extracts were washed with saturated aqueous sodiumhydrogen carbonate (2×100 ml), followed by water (100 ml) and finallydried (Mg SO₄). After the removal of the solvent the product waspurified by column chromatography on silica gel, eluting with a 3:1mixture of chloroform: petroleum fraction (bp 60°-80° C.). Theappropriate fractions containing the product were concentrated andrecrystallised from 95% aqueous ethanol to yield the final nitrileproduct as a white crystalline solid.

R═C₉ H₁₉ : yield=1.7 g (71%), mp 55.0° C.; _(D) ²⁴ +55°.

R═C₁₀ H₂₁ O: yield=0.92 g (62%), mp 98.5° C.; _(D) ²⁴ +6.5°.

EXAMPLE 2

Preparation of: ##STR51## using Route 2

Step 2(1)

To a stirred mixture of the ethyl 4-hydroxybenzoate (0.063 mol) and2,3-dihydropyran (0.25 mol) in ethyl acetate (80 ml) was added dropwisea saturated solution of hydrogen chloride in ethyl acetate (5 ml). Afterthe addition the reaction mixture was stirred for 24 hours at roomtemperature. The mixture was then washed with 10% aqueous sodiumhydroxide (2×50 ml), followed by water (2×50 ml) and finally dried(MgSO₄). After removal of the solvent by distillation under reducedpressure the oily residue was purified by distillation under reducedpressure to give a colourless liquid.

Yield=10.4 g (66%) bp 120°-25° C./0.1 mm Hg (Short path distillation).

Step 2(2)

A solution of potassium hydroxide (0.076 mol) in water (10 ml) was addedto a solution of the product of step 2(1) (0.038 mol) in C₂ H₅ OH (50ml). The mixture was heated under reflux for 3 hours. On cooling, thesolvent was removed by distillation under reduced pressure. Ice-water(100 ml) was added to the residue, and whilst being vigorously stirredand cooled below 10° C., 50% aqueous hydrochloric acid was added untilthe acidity of the mixture reached about pH 3. The product was extractedinto ethyl acetate (2×100 ml) and the combined organic extracts werewashed with water (2×100 ml) and dried (Mg SO₄). After removal of thesolvent the crude material was crystallised from 2:1 toluene: Petroleumfraction (bp 80°-100° C.) to give the carboxylic acid as white crystals.

Yield=5.8 g (69%), decomposed on heating at 145° C.

Step 2(3)

This step was performed using the product of Step 1(1) (the benzyl esterof S-(+)-lactic acid) in a method analogous to step 1(2) (esterificationof the lactic acid alpha-hydroxy group) using the carboxylic acidprepared in step 2(2). The product as obtained by column chromatographywas used in subsequent steps without further purification.

The product had mp below 20° C.; [α]_(D) ²⁴ +18°.

Step 2(4)

A solution of oxalic acid (0.0031 mol) in water (8 ml) was added to theproduct of step 2(3) (0.0156 mol) and the while was gently refluxed for2 hours. The solution was cooled and the solvent was removed bydistillation under reduced pressure. The residue was heated with water(50 ml) and the product was extracted into ether (2×50 ml), and thecombined ether extracts were washed with water (50 ml) and dried (MgSO₄). The oily crude product (single spot on tlc) was used for step 2(5)without further purification.

Yield=4.56 g (95%); [α]D²⁴ +15°.

Step 2(5)

This step was performed using a DCC method of esterification analogousto that used in step 1(2) but using the phenol product of step 2(4)instead of the benzyl lactate for esterification with the4-R-biphenyl-4'-carboxylic acid.

R=C₉ H₁₉ O; C 104°(S_(c) 90°) S_(A) 133.5°Ch 135.5°l[α]_(D) ²⁴ +6.9°.

Step 2(6)

This step involved three separate steps (denoted (a), (b) and (c) below)analagous to steps 1(3), 1(4) and 1(5). The properties of the productsof each of these separate steps for R═C₉ H₁₉ O are as follows:

(a) C149 S_(A) 198 l; [α]_(D) ²⁴ +17.6°.

(b) C180 S_(A) 198 l; [α]_(D) ²⁴ +15.0°.

(c) C121 S_(C) 132 S_(A) 181 l; [α]_(D) ²⁴⁻ 2.9°.

EXAMPLE 3

Preparation of ##STR52##

Step 3(1)

(ref Stocker J Org Chem 27, 2288, (1962)).

A mixture of L-(+)-mandelic acid (10 g), acetic acid (1 ml) and 5%Rh/Al₂ O₃ (1.95 g) in methanol (70 ml) was stirred under hydrogen (30atm) until the uptake of hydrogen was complete. The catalyst wasfiltered off and the solvent was removed. Recrystallisation from carbontetrachloride gave the cyclohexyl compound as a white crystalline solid.

Yield=85%; mp=128° C.

Step 3(2)

(ref S. S. Wang J-Org-Chem, 41, 3258, (1976)

A solution of the product of step 3(1), (5 g) in the minimum volume of4:1 ethanol: water was titrated to pH 7 with aqueous caesium carbonate(20% W/V). The solution was then evaporated to dryness and the lasttraces of water were removed by co-distillation with sodium-driedbenzene (2×100 ml). The residue was dissolved in sieve-dried DMF (100ml) and benzyl bromide (5.3 g) was added, with stirring. Stirring wascontinued for 12 hours after which time the precipitate caesium bromidewas filtered off and the solvent was removed under reduced pressure.Water was added to the residue, and the product was extracted into ethylacetate (100 ml) and the extracts were dried (MgSO₄). Purification wasby column chromography on silica gel using 1:3 ethyl acetate/petroleumfraction (bp 60°-80° C.) or eluent, followed by recrystallisation frompetroleum fraction (bp 40°-60° C.).

Yield=79%; mp 47° C.

Step 3(3)

(ref A. Hassner, V. Alexanian, Tetrahedron, 46, 4475, (1978))

A solution of the appropriate carboxylic acid, in this casen-4-octyloxybiphenyl-4-octyloxybiphenyl-4'-carboxylic acid (10 m mol),the product of step 3(2) (11 m mol), DCC(11 m mol) and N--PPy (1 mol) insieve-dried dichloromethane (50 ml) was stirred with exclusion ofmoisture. The progress of the reaction was followed by tlc on silicagel, eluting with 2:1 chloroform: petroleum fraction (bp 60°-80° C.).The mixture was filtered off and the filtrate was washed successivelywith water (3×50 ml), 5% acetic acid (3×50 ml) and again water (3×50ml), then finally dried (MgSO₄). The product (an oil) was purified bycolumn chromatography on silica gel, eluting with 2:1 chloroform:petroleum fraction (bp 60°-80° C.) to give the product as colourlessliquid.

Yield=67%; [α]_(D) ²⁵ +5.3°.

Step 3(4)

A mixture of the product of step 3(3) and (1 g) and 5% Pd--C in ethanol(25 ml) was stirred under an atmosphere of hydrogen until uptake of thegas had ceased. The catalyst was filtered off and the solvent removed bydistillation under reduced pressure. Purification of the crude productwas by column chromatography on silica gel, eluting with a 5:1chloroform:methanol. Recrystallisation from petroleum fraction (bp60°-80° C.) gave the carboxylic acid as a white crystalline solid.

Yield=96%: mp=83° C.; [α]_(D) ²⁵ -39.5°.

Step 3(5)

A suspension of the product of step 3(4) (0.5 g) in a mixture ofsodium-dried benzene (25 ml), oxalyl chloride (0.25 g) and DMF (onedrop) was stirred for 2 hours. The solvent was removed by distillationunder reduced pressure and the residue was dissolved in dry diglyme (50ml). Aqueous ammonia (d=0·88, 10 ml) was added to this solution wasvigorous stirring during 30 min, and stirring was continued for afurther 30 minutes. The mixture was diluted with water (100 ml) and theprecipitated amide was filtered off. Recrystallisation from 4:1ethanol:water gave the product as a white powder.

Yield=82%, mp 126° C.

Step 3(6)

A solution of the product of step 3(5) (0.47 g), thionyl chloride (1.2g) and dry DMF (30 ml) was stirred for 8 hours. The reaction mixture wasthen poured into water (50 ml) and the nitrile was extracted into ether(3×50 ml). The combined ether extracts were washed with saturated sodiumhydrogen carbonate solution and dried (MgSO₄). Purification of the crudenitrile was by column chromatography on silica gel, eluting with 1:5ethyl acetate:petroleum fraction (6 p 60°-80° C.). Recrystallisationfrom 4:1 ethanol:water gave the nitrile as a white crystalline solid.

Yield=78%, mp 58.5° C.; [α]_(D) ²⁵ -10.5.

EXAMPLE 4

Ferroelectric smectic liquid crystal mixture containing compounds ofFormula I in hosts which are compounds of formula 4.1

Mixture A ##STR53##

Transition temperatures; S_(?) ca. 40 S_(C) 66.8 S_(A) 111.3 N 134.7 I.

    ______________________________________                                        Ferroelectric properties:                                                     Temperature   Extrapolated Ps                                                                           Tilt angle of                                       (°C.)  (nC cm.sup.-2)                                                                            S.sub.C phase (°)                            ______________________________________                                        65             56         2.5                                                 60            133         5.5                                                 40            315         9.5                                                 ______________________________________                                    

The extrapolated pitch of the S_(C) phase of the mixture was 0.201 μm.

Mixture B ##STR54##

Transition temperatures: S_(?) 45 S_(C) 56.1 S_(A) 115 N 134.8 I.

    ______________________________________                                        Ferroelectric properties:                                                     Temperature   Extrapolated Ps                                                                           Tilt angle of                                       (°C.)  (nC cm.sup.-2)                                                                            S.sub.C phase (°)                            ______________________________________                                        55            15.5        0.75                                                50            133         4.3                                                 ______________________________________                                    

The extrapolated pitch of the S_(C) phase of the mixture was 0.291 μm.Mixtures C to G below were all based on a smectic host having acomposition: ##STR55##

Mixture C ##STR56##

Transition temperatures: S_(C) --S_(A) 64°, S_(A) --Ch 109.6°, CH--I135.2°-136.8° (S_(C) at room temp.)

Mixture C (contd.)

    ______________________________________                                        Ferroelectric properties:                                                     Temperature °C.                                                                   Ps nCcm.sup.-2                                                                           Temperature °C.                                                                     Ps nCcm.sup.-2                             ______________________________________                                        31         3.47       45           21.52                                      32         6.94       50           18.75                                      33         29.17      55           13.89                                      34         29.86      60           9.37                                       35         28.47      63           4.34                                       40         24.30                                                              ______________________________________                                    

Mixture D ##STR57##

Transition Temperatures: S--S_(C) 32°, S_(C) --S_(A) 81° C., S_(A) --Ch118.8°, Ch--I 139.2°-140.5°.

    ______________________________________                                        Ferroelectric properties:                                                     Temperature °C.                                                                   Ps nCcm.sup.-2                                                                           Temperature °C.                                                                     Ps nCcm.sup.-2                             ______________________________________                                        31         18.75      50           27.08                                      32         44.44      55           25.00                                      33         40.28      60           21.53                                      34         38.89      65           18.40                                      35         36.81      70           14.93                                      40         33.33      75           10.41                                      45         30.56      80           1.39                                       ______________________________________                                    

Mixture E ##STR58## Mixture E. (contd.)

Transition temperatures: S--S_(C) 11°, S_(C) --S_(A) 58.7°, S_(A) --N100°, Ch--I 124°-125.4°.

    ______________________________________                                        Ferroelectric properties:                                                     Temperature °C.                                                                   Ps nCcm.sup.-2                                                                           Temperature °C.                                                                     Ps nCcm.sup.-2                             ______________________________________                                        10         48.61      40           22.92                                      15         41.67      45           19.79                                      20         36.81      50           15.63                                      25         33.33      55           9.55                                       30         29.86      58           2.78                                       35         25.69                                                              ______________________________________                                    

Mixture F ##STR59##

Transition temperatures: S_(C) --S_(A) 62.56°, S_(A) --Ch 81.4°, Ch--I121°-123.2° (room temp S_(C)).

    ______________________________________                                        Ferroelectric properties:                                                     Temperature °C.                                                                   Ps nCcm.sup.-2                                                                           Temperature °C.                                                                     Ps nCcm.sup.-2                             ______________________________________                                        -5         22.2       35           10.76                                       0         18.75      40           9.72                                        5         17.71      45           8.51                                       10         16.67      50           7.46                                       15         15.63      55           5.90                                       20         14.24      60           3.75                                       25         13.19      62           2.57                                       30         12.15                                                              ______________________________________                                    

Mixture G ##STR60## In this mixture the two optically active compoundsinduced the appearance of Ch phases of opposite helical twist sense andhence the mixture is pitch compensated.

Transition temperatures: S_(C) --S_(A) 63.4°, S_(A) --N 84.2°, N--Ch100°, Ch--I 120.4°-122.2 (room temperature S_(C)).

    ______________________________________                                        Ferroelectric properties                                                      Temperature °C.                                                                   Ps nCcm.sup.-2                                                                           Temperature °C.                                                                     Ps nCcm.sup.-2                             ______________________________________                                        -10        22.22      30           13.54                                      -5         21.52      35           11.81                                       0         19.44      40           10.94                                       5         18.40      45           9.54                                       10         17.36      50           8.16                                       15         16.67      55           6.42                                       20         15.28      60           3.96                                       25         14.24      63           0.28                                       ______________________________________                                    

EXAMPLE 5 ##STR61## Step 4(1)

A cold solution of sodium nitrite (26.4 g, 0.384 mol) in water (105 ml)was added dropwise to a stirred and cooled solution of L-valine (30.0 g,0.256 mol) in 0.5 M sulphuric acid (390 ml) during 3 hours, maintainingthe temperature between 0° C. and -2° C. The reaction mixture was leftstirring at room temperature overnight, then adjusted to pH 6 by addingsolid sodium bicarbonate. The solution was concentrated under reducedpressure at 50° C. to about 150 ml. The solution was acidified to pH 3with 40% H₃ PO₄ and the crude product was extracted into THF (2×200 ml).The THF solutions were washed with brine, dried (Mg SO₄) andconcentrated under reduced pressure at 50° C. to give an oil.

The crude product was taken in water (105 ml) and decolourized withcharcoal at room temperature. A concentrated solution of sodiumhydroxide was added dropwise to the cold solution adjusting the pH to4.5-5. Acetone (3 times the volume of the aqueous solution) was addedand the precipitate which formed was filtered off and dried (in vacuoCaCl₂).

yield =22 g (61%) [α]_(D) ²⁰ =-13.95° (H₂ O).

Step 4(2)

A mixture of the product of step 4(1) (10.0 g 72 mmol), benzyl bromide(12.2 g 72 mmol) and sieve dried DMF (120 ml) was stirred at roomtemperature for 24 hours. The DMF was removed under reduced pressure (at50°-55° C.) and the remaining suspension was diluted with ether (100 ml)and filtered. The filtrate was washed successively with water, sodiumbicarbonate solution, water, and dried (MgSO₄). After distilling off thesolvent (below 55° C.) the crude product was obtained.

yield=14.4 g (96%).

The crude product was purified by distillation at 135°-140° C./0.6-0.65mm Hg.

Step 4(3)

To a stirred mixture of 4'-octyloxy-4-carboxylic acid (10.8 g 0.033mol), the product of step 4(2) (6.9 g 0.033 mol) and N--PPY (0.49 g0.033 mol) in sieve-dried dichloromethane was slowly added a solution ofDCC (7.5 g 0.036 mol) in sieve-dried dichloromethane (50 ml) over aperiod of 20 min.

The reaction mixture was stirred for 6 hours at room temperature. TheN,N-dicyclohexylurea was filtered off and the filtrate was washedsuccessively with water, 5% aqueous acetic acid, water and finally dried(MgSO₄). After removal of the solvent, the crude diester was purified bycolumn chromatography using silica gel with 4:1 dichloromethane:lightpetroleum (bp 60°-80° C.) as eluent, to give a viscous liquid product.

yield=12.5 g (74%).

Step 4(4)

The product of step 4(3) (12.5 g 24.2 mmol) was dissolved in ethylacetate (160 ml) and 5% Pd on charcoal (200 mg) was added. The mixturewas stirred overnight under an atmosphere of hydrogen (the reaction wasmonitored by TLC). After hydrogenolysis was complete (ca 550 ml of H₂),the catalyst was filtered off and the filtrate was evaporated to drynessto give a solid product. The solid gave a single spot on TLC and wasused without further purification.

yield=9.7 g (95%) mp=80°-83° C.

Step 4(5)

The carboxylic acid from 4(4) (9.4 g 22.06 mmol) was initially convertedinto the acid chloride by reacting with oxalyl chloride (5.75 g 44 mmol)and sieve dried DMF (2 drops) in sodium--dried benzene (25 ml) for 3hours at room temperature. The excess of oxalyl chloride and the solventwere removed by distillation under reduced pressure. The crude acidchloride was dissolved in diglyme (10 ml) and added to an aqueoussolution of ammonia (5 g=0.88, 100 ml) with stirring. After the additionthe reaction mixture was stirred for 1/2 hour at room temperature, thenthe product was filtered off, washed with water and dried (in vacuoCaCl₂).

yield=9.4 g (100%) mp=95°-97° C.

Step 4(6)

A mixture of thionyl chloride (26.3 g 221 mmol) and sieve-dried DMF (100ml) was added dropwise during 30 minutes to a vigorously stirredsolution of the amid from step 4(5) (9.0 g, 22.1 mmol) in sieve-driedDMF (100 ml). After the addition the reaction mixture was left stirringat room temperature for 8 hours, was then poured onto ice-water and theproduct was extracted into ether (2×300 ml). The ether extracts werewashed successively with a saturated solution of sodium bicarbonate andwater, and then dried (MgSO₄). After After removal of the solvent theproduct was purified by column chromatography on silica gel, elutingwith 1:3 ethyl acetate: light petroleum (bp 40°-60° C.).

yield=8.3 g (97%).

The product from the column was recrystallised from light petroleum (bp40°-60° C.) to give a white crystalline solid.

mp=66.9° C. [≢]_(D) ²⁰ =-3.1° (CHCl₃).

The compounds listed below were prepared using an identical method withthe appropriate carboxylic acid in step 4(3) and the amino acidindicated in step 4(1).

    ______________________________________                                        General formula:                                                               ##STR62##                                                                                                       Liquid                                                                        Crystal                                    R      B             [α].sub.D.sup.20 = (CHCl.sub.3)                                                       Transitions                                ______________________________________                                        C.sub.8 H.sub.17 O                                                                   CH.sub.2 CH(CH.sub.3).sub.2                                                                 -17.5° K 46 I                                     (L-Leucine, S-(+)-Leucine)                                                    C.sub.8 H.sub.17 O                                                                   CH(CH.sub.3).sub.2                                                                           -3.1° K 67 I                                     (L-Valine, S-(+)-Valine)                                                      C.sub.8 H.sub.17 O                                                                   *CH(CH.sub.3)CH.sub.2 CH.sub.3                                                               -5.4° K 74 I                                     (L-Isoleucine; (2S,3S)-(+)-2-amino-3-methylpentanoic acid)                    C.sub.8 H.sub.17 O                                                                   (CH.sub.2).sub.3 CH.sub.3                                                                   -10.6° K 59 I                                     (L-Norleucine; (S)-(+)-2-aminohexanoic acid)                                  ______________________________________                                    

EXAMPLE 6

Preparation of: ##STR63## using Route 6.

Step 6(3)

4-n-decyl-4'-hydroxybiphenyl (0.02 mol), tosyl lactate (0.024 mol) andanhydrous potassium carbonate (0.024 mol) in sieve-dried acetonitrile(100 ml) was gently refluxed with vigorous stirring for 20 hr. Thecooled reaction mixture was poured into cold water (200 ml) andextracted with ether (2×150 ml). The combined ether extracts were washedwith water (100 ml), cold 5% aqueous NaOH (100 ml), water (2×100 ml) anddried (MgSO₄). After removal of the solvent, the solid residue wasrecrystallised from 95% aqueous ethanol to yield the product ascolourless crystals.

Yield 5.5 g (67%), mp 38° C., [α]_(D) ²⁴ +91.1° (CHCl₃).

Step 6(4)

The product of step 6(3) (0.012 mol), KOH (0.0144 mol) in water (15 ml)and ethanol (50 ml) was gently refluxed for 1 hr. Excess solvent wasremoved under reduced pressure and the residue was diluted with coldwater (50 ml) and them carefully acidified by the addition of dilute HCluntil a pH of about 2 was obtained. The mixture was extracted with ether(3×50 ml) and the combined ether extracts were washed with water (50 ml)and dried (MgSO₄). After removal of the solvent, the solid residue wasrecrystallised from petroleum ether (80°-100° C.).

Yield 4.3 g (93%), mp 110.5° C., [α]_(D) ²⁴ +8.4° (CHCl₃).

Step 6(5)

This was carried out using a similar method to that of Route 1 step 4.The starting materials were the product of step 6(4) (0.011 mol), oxalylchloride (0.021 mol) in benzene (60 ml), DMF (2 drops) and 35% aq. NH₃in diglyme (100 ml). The crude product was crystallised from petroleumether (100°-120° C.).

Yield 3.6 g, (88%), mp 171° C.

Step 6(6)

This was carried out using a method similar to that of Route 1 step 5.The starting materials were the product of step 6(5) (0.0087 mol),thionyl chloride (0.0087 mol) in DMF (80 ml). The crude product waschromatographed using silica gel and eluted with CH₂ Cl₂. The purifiedmaterial was crystallised from ethanol.

Yield 2.6 g, (84%), mp 66° C., [α]_(D) ²⁴ +96.8° (CHCl₃).

EXAMPLE 7

Using the methods outlined in the description above the followingcompounds were also prepared: ##STR64## Some of their properties arelisted below: A. solid--isotropic 84.3°, [α]_(D).sup.° -28.1 (CHCl₃)

B. solid¹ --solid² 29.4°, solid--isotropic 32.2° [α]_(D) ²⁰ -4.8°(CHCl₃)

C. liquid, mp below -20° C. [α]_(D) ²⁰ -16.8° (CHCl₃)

D. solid--S_(C) 102°, S_(C) --S_(A) 145°, S_(A) --I 154.6 [α]_(D) ²⁰-9.35° (CHCl₃).

EXAMPLE 8

Ferroelectric smectic liquid crystal mixtures containing compounds offormula I and 4.1.

In the data below, the material H1 has a composition: ##STR65## and thenematic material E7 has a composition: ##STR66##

Properties of mixtures containing compounds of formula I and H1 arelisted in tables 5 and 6 where the following symbols and abbreviationsare used

Ps=extrapolated spontaneous polarisation (nCcm⁻²)

N*p=chiral nematic pitch in E7 (μm)

pPs=N*p×Ps

SOP/_(SON) =sense of N* helical pitch and polarisation of S_(C) * phase

C₉, C₉ O etc. are abbreviations for C₉ H₁₉, C₉ H₁₉ O etc.

                                      TABLE 5                                     __________________________________________________________________________                                                        Trans. Temps.                                                P.sub.S                                                                             N* p   SOP/                                                                              (10% in H1)                                                  nCcm.sup.-2                                                                         μm                                                                            pP.sub.S                                                                          SON*                                                                              N S.sub.A                                                                         S.sub.C                                                                           S.sub.7           __________________________________________________________________________     ##STR67##                         180   0.20                                                                             36  L.sup.+                                                                           112 67  40                 ##STR68##                         137          L.sup.+                                                                           115 81  33                 ##STR69##                          70   0.58                                                                             41  L.sup.+                                                                           133 78  49                 ##STR70##                         139   0.27                                                                             38  D.sup.+                                                                           112 72  25                 ##STR71##                         164   0.53                                                                             87  D.sup.+                                                                           111 74  23                 ##STR72##                         125   0.22                                                                             28  D.sup.+                                                                           110 59  27                 ##STR73##                         --    0.15                                                                             --  D                              ##STR74##                         112   0.60                                                                             67  D.sup.+                                                                           105 58  22                 ##STR75##                                      D.sup.+                                                                           128 63  45                 ##STR76##                          2.5  0.68                                                                              2  .sup.+                                                                            101 80  37                __________________________________________________________________________

Table 6 below shows properties of fast switching ferroelectric smecticliquid crystal mixtures based upon the following materials: ##STR77##

In table 6 proportion of host etc are in weight %, phase transition in°C., tilt in °, PW means minimum pulse width *us) to switch, and ACmeans the peak voltage to latch (V), Ps and tilt are at 25° C.

Table 6 demonstrates the fast switching time of the mixtures by the lowvalues of the minimum pulse width to switch.

FIG. 7 shows graphs of Ps against temperature (°C.) for various of themixtures listed in table 6. The symbols in table 6 identify the graphs.

EXAMPLE 9

Ferroelectric smectic liquid crystal mixtures containing compounds offormula I and 4.3.

A mectic host H2 was prepared having a composition: ##STR78##

                                      TABLE 6                                     __________________________________________________________________________                   Transitions                                                    H1 %  Addv %                                                                             Dop %                                                                             I    N    SA   SC     S Ps                                                                              Tilt                                                                             PW AC                             __________________________________________________________________________      88.75                                                                             10   1.25  139  89    84          5                                                                              25 -- --                             •                                                                         87.5                                                                              10   2.5   136  92    83  8      10                                                                              29 130                                                                              16                               85  10   5     132  96    75  0.5    21                                                                              23 150                                                                              30                             ◯                                                                   80  10   10    126  97    55  -2     36                                                                              21  50                                                                              40                             □                                                                    75  20   5     120  73    60  -25    20                                                                              21  60                                                                              20                               72.5                                                                              25   2.5   118  --    56          8                                                                              27 500                                                                              15                               77  20   3     123  73    66         12                                                                              -- 100                                                                              16                               85.sup.a                                                                          --   10    129  106   55  24     44                                                                              -- -- --                               79.sup.b                                                                          11   6.25  123  92    57         26                                                                              22  60                                                                              40                               80.sup.c                                                                          10   9.5   124  95    60  2      35                                                                              21  50                                                                              --                             __________________________________________________________________________     .sup.a plus 5 wt % of compensator A                                           .sup.b plus 3.75 wt % of compensator A                                        .sup.c plus 0.5 wt % of compensator B                                    

Mixture H ##STR79## has phase transitions (°C.)

I 128 N* 84 S_(A) 64 S_(C) * <-20.

Mixture I ##STR80## The configuration of the two optically activecompounds was chosen to be such that they induced the appearance ofchiral smectic phases of opposite helical twist sense.

The mixture had phase transitions (°C.)

I 145 N* 114 S_(A) 59.7 S_(C) * 10 S_(?).

An example of the use of a compound of Formula I in a liquid crystalmaterial and device embodying the present invention will now bedescribed with reference to FIG. 8.

In FIG. 8 a liquid crystal cell comprises a layer 1 of liquid crystalmaterial exhibiting a chiral smectic phase sandwiched between a glassslide 2 having a transparent conducting layer 3 on its surface, e.g. oftin oxide or indium oxide, and a glass slide 4 having a transparentconducting layer 5 on its surface. The slides 2,4 bearing the layers 3,5are respectively coated by films 6,7 of a polyimide polymer. Prior toconstruction of the cell the films 6 and 7 and rubbed with a soft tissuein a given direction the rubbing directions being arranged parallel uponconstruction of the cell. A spacer 8 e.g. of polymethyl methacrylate,separate the slides 2, 4 to the required distance, e.g. 5 microns.

The liquid crystal material 1 is introduced between the slides 2,4 byfilling the space between the slides 2, 4 and spacer 8 and sealing thespacer 8 in a vacuum in a known way. Preferably the liquid crystalmaterial is in the smectic A, nematic or isotropic liquid phase(obtained by heating the material) when it is introduced between theslides 2,4 to facilitate alignment of the liquid crystal molecules withthe rubbing directions on the slides 2,4.

A polarizer 9 is arranged with its polarization axis parallel to therubbing direction on the films 6,7 and an analyzer (crossed polarizer)10 is arranged with its polarization axis perpendicular to that rubbingdirection.

When a square wave voltage (from a conventional source not shown)varying between about +10 volts and -10 volts is applied across the cellby making contact with the layers 3 and 5 the cell is rapidly switchedupon the change in sign of the voltage between a dark state and a lightstate as explained above.

In an alternative device (not shown) based on the cell constructionshown in FIG. 8 the layers 3 and 5 may be selectively shaped in a knownway, e.g. by photoetching or deposition through a mask, e.g. byphotoetching or deposition through a mask, e.g. to provide one or moredisplay symbols, e.g. layers, numerals, words or graphics and the likeas conventionally seen on displays. The electrode portions formedthereby may be addressed in a variety of ways which include multiplexedoperation.

The liquid crystal material 1 may be any one of the mixtures describedin the preceding examples.

We claim:
 1. An optically active dopant suitable for inclusion in a ferroelectric smectic liquid crystal mixture, said dopant having the structure ##STR81## in which X is a group having the formula: ##STR82## where R is selected from hydrogen, or C₁₋₁₂ alkyl or alkoxy, each of the rings D is the same or different and are independently selected from phenyl and halogen substituted phenyl, A is selected from phenyl, halogen and substituted phenyl and trans-cyclohexyl, d is 0 to 1, and B is selected from C₁₋₁₂ straight chain or branched chain alkyl and alkyl alicyclic.
 2. The optically active dopant according to claim 1 where X is ##STR83##
 3. The optically active dopant according to claim 2 where B is: ##STR84## where t is 0 and an integer 1-6, and n and m are the same or different and have values 1-6.
 4. The optically active dopant according to claim 2 where B is straight chain alkyl.
 5. The optically active dopant according to claim 4 where said straight chain alkyl is CH₃.
 6. The optically active dopant according to claim 2 where B is ##STR85## .
 7. The optically active dopant according to claim 1 having the structure ##STR86## where t is 0 or an integer 1-6, and n and m are the same or different and have values 1-6.
 8. A ferroelectric smectic liquid crystal material being a mixture of at least two compounds where at least one compound is a compound according to claim 1 and the other compound selected from: ##STR87## where R^(A) and R^(B) are independently C₁₋₁₂ n-alkyl or n-alkoxy or an optically active alkyl or alkoxy group.
 9. A ferroelectric smectic liquid crystal material being a mixture of at least two compounds where at least one compound is a compound according to claim 1 and the other compound has the formula: ##STR88## where R^(A) and R^(B) are independently C₁₋₁₂ n-alkyl or n-alkoxy. 